class Solution3 {

    boolean[][] vis;
    int m, n;
    char[] word;
    int[] dx = {0,0,1,-1};
    int[] dy = {1,-1,0,0};


    public boolean exist(char[][] board, String _word) {
        m = board.length; n = board[0].length;
        word = _word.toCharArray();
        vis = new boolean[m][n];

        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if(board[i][j] == word[0]){
                    vis[i][j] = true;
                    if(dfs(board, i, j, 1) == true) { return true;}
                    vis[i][j] = false;
                }
            }
        }
        return false;
    }

    public boolean dfs(char[][] board, int i, int j, int pos){
        if(pos == word.length){
            return true;
        }

        for(int k = 0; k < 4; k++){
            int x = i + dx[k], y = j + dy[k];
            if(x >= 0 && x < m && y >= 0 && y < n && !vis[x][y] && board[x][y] == word[pos]){
                vis[x][y] = true;
                if(dfs(board, x, y, pos + 1) == true) { return true;}
                vis[x][y] = false;
            }
        }
        return false;
    }
}